There is increasing public awareness of the harmful health effects of exposure of human skin in prolonged or intense sunlight, especially for fair-skinned persons and those with limited ability to repair photochemical DNA damage. Not only does light cause skin ageing and wrinkling, but malignant melanomas and other cancers have been shown to correlate with exposure to light in certain portions of the solar spectrum. It is the goal of this research to develop the fundamentals for an inexpensive, nontoxic actinometer to monitor the cumulative dosage of harmful light so that skin damage and skin cancers can be minimized. Preliminary investigations have suggested that aqueous solutions of cycloalkanones such as cyclohexanone offer promise as a chemical actinometer system that may be especially useful in monitoring those wavelengths of light most likely to cause skin damage. The cumulative dose of sunlight exposure could be determined by laboratory methods, such as gas chromatography. Alternatively, the solutions could be packaged in consumer- wearable devices so that the pH change produced by the solar reaction would cause an indicator to change color, allowing persons to continuously measure and thereby better limit their exposure to sunlight. An attractive feature of the proposed devices is that sun screen agents could be applied over them, allowing an accurate measure of potential skin damage. The proposed research project will characterize the effect of wavelength and temperature on the quantum yield photochemical reaction for a series of cyclohexanones in aqueous solutions. Higher molecular weight derivatives of cyclohexanone or other cycloalkanones solubilized in micelles or synthetic vesicles will also be investigated. Such systems could be tailored to respond to specific wavelengths of light or for long- or short-term exposures.